维生素C含量的测定实验报告.doc

曹威 5090809047 F0908002 The quantity measurement of ascorbic acid and the comparison of ascorbic acidIntroductionVitamin C is one of the essential vitamin among all vitamin. Vitamin C also ascorbic acid. The name is derived from a- (meaning no) and scurvy, the disease caused by a deficiency of vitamin C. It has the most important function on regulating the metabolism in the human body even in the animal. According to the recently research, it also have the ability to prevent the tumor and blocking the chemical carcinogen.We design this experiment to figure out the relationship between the temperature and the VC content of the nature Fresh Tangerine juice.Through titrate with standard ascorbic acid solution (1mg/ml)，we only find there is relationship between temperature and VC content，but we dont know what it is.We are willing to do in-depth study on this item to make the law clear. Key words : Ascorbic acid, 2,6-Dichloro-phenol-indeophenol (DCPIP),Temperature1 PrefaceVitamin C mainly exists in fresh fruits and vegetables. Among all types of fruits, kiwi contains most vitamin C while lemon and orange also rich in vitamin C. Besides, vitamin C is highly content in chili and also found in other kind of vegetables like tomato, radish. In wild plants, Vitamin C most abundant in a species of roses, which contains 2800mg per 100g.1.1 Characteristic of the ascorbic acidVitamin C is a colorless crystal, insoluble in water and ethanol, heat labile , unstable in the alkaline solution, more stable under dry conditions and susceptible to oxidation after explode to sunlight. The existence of some heavy metals like trace copper, iron cause vitamin C easier decompose due to oxidation, so should avoid contact with alkali and copper when cooking vegetables. Therefore, vitamin C should be stores in dry, dark place at low temperature. In 1928, Arctic anthropologist Vilhjalmur Stefansson proved that fresh meat which is minimally cooked also contains vitamin C.1.2 The reducibility of the ascorbic acid Ascorbic acid is a strong agent. A commonly-used oxidizing agent is the dye 2,6-dichlorophenol-indophenol, or DCPIP for short. The blue dye is run into the ascorbic acid solution, which turns pink in the acid conditions, until the solution is decolorized. In a titration, when all the ascorbic acid in the solution has been used up, means ascorbic acid all in the oxidation state, there will not be any electrons available to reduce the DCPIP and the solution will remain pink due to the reduced form of DCPIP(DCPIPH). The end point is a pink color that persists for 10 seconds or more. Pharmacological experiments suggest that DCPIP may serve as a pro-oxidant chemotherapeutic targeting human cancer cells in an animal model of human melanoma; DCPIP-induced cancer cell death occurs by depletion of intracellular glutathione and upregulation of oxidative stress. DCPIP (blue) + H+ DCPIPH (pink)DCPIPH (pink) + Vitamin C DCPIPH2 (colorless)C6H8O6 + C12H7NCl2O2 C6H6O6 + C12H9NCl2O22 Experiment material and the experimentation2.1 Reagent and the apparatus2.1.1 Reagent(1) 2% oxalic acids solution： Using 2g of the oxalic acid solid and dissolving in 100ml distilled water (2) 1% oxalic acids solution： Using 1g of the oxalic acid solid and dissolving in 100ml distilled water(3) Standard ascorbic acid solution (1mg/ml)： Precisely take the 100mg of the pure ascorbic acid and dissolve it in the 1% of oxalic acid , and dilute it to 100ml after that keeping it in the brown glass flask, refrigerated. It is better to make it before using it.(4) 0.1% 2,6-dichloro-phenol-indophenol： Using 250mg 2,6-diochlor-phenol-indophnol(DCPIP) dilute it in 150ml hot water in which contain 52mg NaHCO3, cooling it and adding water to dilute to 250ml. It can keep it for one week in refrigerating it in 4 Celsius degree. Titrate the DCPIP with the ascorbic acid every time before using.2.1.2 Material and equipment(1) Material： Fresh Tangerine(2) Equipment： Conical beaker 100ml (x2), Pipet 10ml(x1), Volumetric flask 100ml (x1) / 250ml (x1) , Microburette 5ml (x1) Picture 1, Funnel, Gauze, MortarPicture 1. Microburette2.2 Procedures2.2.1 Operation methods(1) Distillation Take a half of a tangerine ，which is weighted ，and 40ml 2% oxalic acid, using the mortar to grind, after that using gauze to filtrate, after that using oxalic acid to wash the gause and using water to dilute the ncorporate filtration to 100ml.(2) TitrationPrecisely absorb 1ml of standard ascorbic acid into the 100ml of erlenmeyer flask, adding 9ml of 1% oxalic acid. Using the microburette to titrate it until pink, if it will keep the colour for at least 15 second it is the end point. We can count out 1ml of the dye equal to how many of volume of the ascorbic acid. The consumed of the dye. ( Taking 10ml of the oxalic acid for the blank control, follow the step above)(3) Sample titration Precisely absorb the sample into seven erlenmeyer flasks ， which of them each contain 10ml, and put it apart in the round bottom flask.After that，heating them in the microwave oven for seven different time，inorder to reach different temporary. After that，using the step of titration above. ( Taking 10ml of the oxalic acid for the blank control, follow the step above ).2.2.2 CountingContent of the ascorbic acid(mg/100g sample) = (VA-VB) x C x T x 100 / (D+W)in the formula above :VA volume of dye used during titration for sample (ml)VB volume of dye used during titration for blank control (ml)C volume of filtrate (ml)D volume of filtrate during titration (ml)T mass of ascorbic acid to reduce 1ml dye (mg)W weight of sample3 Result of the experiment3.1 Experiment data(1) Mass of the pieces tangerine : 40.165g(2) Titration of the standard ascorbic acid using the DCPIP dye :Standard solution1stBlankConcentration of the standard (c)1mg/ml1mg/1mlVolume of dye consumed (ml)1.98 ml0.04 mlMass of ascorbic acid oxidated by 1ml of dye1/(1.98-0.04)=0.515 the titration of the standard ascorbic acid(3) Titration of the filtrate of the tangerine by using the DCPIP dye :Filtrate1st2st3st4st5st6st7stTemperature()20.336.043.259.546.184.496.0Va4.944.334.985.044.484.014.96Vb0.740.000.080.74Volume of dye consumed (ml)64.804.483.934.22Content of the ascorbic acid in the samples (mg/100g)5.335.245.045.41 the titration of the tangerine filtrate3.2 Counting Experiment dataUsing the formula of 2.2.2 to count out the content ascorbic acid of the tangerine .The content of ascorbic acid of the tangerine (mg/100ml) : 5.33mg / 100g Using Origin 8.0 to manipulation data.The figure followed： the figure for Temperature-VC 3.3 Result of the experimentFollowing the data above, we can conclude that the content of senven samples in different temperature , in contrast,the temperature erratically affect the content of the VC in samples. As a result ,our tests cant show the true relationship between temperature and the VC content. Tangerine is only have 5.33 mg of ascorbic acid per 100mg.3.4 Result analysisComparison of the result of the experiment, we are now can make any conclusion .Compare with theoretic value of content of the ascorbic acid in tangerine, we can know that is a bit difference with it. The theoretic value is 25 30mg per 100mg and this can demonstrate that content of ascorbic acid in the tangerine is depends on their different breed. This data is only for reference.According to some documents I got on the Internet,the temperature affect the VC content in regular way.Often projects find that orange juices made from frozen concentrated orange juice (FCOJ) have the highest vitamin C levels as compared to freshly squeezed or not-from-concentrate (NFC) juices.In orange juice containers, vitamin C loss was due to oxidation by a residual air layer trapped within the container during processing. The loss was faster in the first 2 weeks and was more evident at higher storage temperatures. Therefore, orange juice must be kept cool to prevent vitamin C degradation as it is excellerated at high storage temperatures.Vitamin C levels depend on six main factors:1 Production factors and climate conditions2 Maturity state and position on the tree3 Type of citrus fruit (species and variety)4 Parameters used for processing into different products5 Type of container6 Handling and storage3.5 Error analysis of experimentation (1) Because of using the mortar to get the extract, even though this is the most simple method, we cannot thoroughly let the ascorbic acid inside tangerine completely dissolve in thee solution, thus caused the experimental result inaccurate.(2) In addition, when using the gauze to filtrate the extract, even if we used the 2% of oxalic acid to wash away the ascorbic acid which was remaining inside the gauze,there will still remaining some juice in the gauze and the remnants of the tangerine.(3) In titration, as a result of the dye(DCPIP) inside the microburette was leaking out between the knob, it was added the volume of the consumed dye.(4) The naked eyes judgement of the end point has brought in experimental error.(5) As the result，cooking affect the VC content in food under the influence of the cooking time and styles of gastronomy. Braise：VC content losing rate range from 8.1 to 33.5 percent Boiled：VC content losing rate range from 15.3 to 19 percent Fried：VC content losing rate range from 10 to 30 percent And the losing rate will raise follow the increasing time of cooking.4 ConclusionThrough this experiment, it has proved that VC content of sample do have something to do with the temperature.Unfortunately，we have not figure out the regular pattern.But it will be an attractive item for us to do more work on.4.1 Vitamin Cs biological significance /wiki/Vitamin_CVitamin C is purely the L-enantiomer of ascorbate; the opposite D-enantiomer has no physiological significance. Both forms are mirror images of the same molecular structure. When L-ascorbate, which is a strong reducing agent, carries out its reducing function, it is converted to its oxidized form, L-dehydroascorbate. L-dehydroascorbate can then be reduced back to the active L-ascorbate form in the body by enzymes and glutathione. During this process semidehydroascorbic acid radical is formed. Ascorbate free radical reacts poorly with oxygen, and thus, will not create a superoxide. Instead two semidehydroascorbate radicals will react and form one ascorbate and one dehydroascorbate. With the help of glutathione, dehydroxyascorbate is converted back to ascorbate. The presence of glutathione is crucial since it spares ascorbate and improves antioxidant capacity of blood.11 Without it dehydroxyascorbate could not convert back to ascorbate.Model of a vitamin C moleculeBlack is carbon, red is oxygen, white is hydrogen4.2 Vitamin Cs Physiological functionIn humans, vitamin C is essential to a healthy diet as well as being a highly effective antioxidant, acting to lessen oxidative stress; a substrate for ascorbate peroxidase; and an enzyme cofactor for the biosynthesis of many important biochemicals. Vitamin C acts as an electron donor for important enzymes:Collagen, carnitine, and tyrosine synthesis, and microsomal metabolism4.3 The comparison within ascorbate and ascorbic acidMineral ascorbates are salts of ascorbic acid. They are powders manufactured by reacting ascorbic acid with mineral carbo